Dogs running loose may have been having to fight for their lives, fight over food, or fight over territory. They would fight your dog if they thought it was taking away what it needed like food,...
in general, there could be two realistic answers to this.
The first as a joke ... none, dogs don't have feet they have paws.
The second answer forgiving the feet/paw issue and presuming you meant...
The owner of any dog that bites should be cited by the police, and the SPCA should probably be called to investigate to make sure that the aggressive dog doesn't need to be removed.